Theories of associative learning are concerned with the factors that governassociation formation when two stimuli are presented together. In this articlewe review the relative merits of the currently influential theories ofassociative learning. Some theories focus on the role of attention inassociation formation, but differ in the rules they propose for determiningwhether or not attention is paid to a stimulus. Other theories focus on thenature of the association that is formed, but differ as to whether thisassociation is regarded as elemental, configural, or hierarchical. Recentdevelopments involve modifications to existing theories in order to account forassociative learning between two stimuli, A and B, when A is accompanied, notby B, but by a stimulus that has been paired with B. The implications of thetheories for understanding how humans derive causal judgments and solvecategorization problems is considered.